Protecting a Continent's Wildlife from Disease

tags: Trypanosoma evansi, parasite, wasting disease, Tabanus, Australia, conservation

A PhD student from James Cook University in Australia hopes her research will help protect Australian wildlife from an exotic wasting disease that could devastate kangaroos and other endemic marsupials.

Kirsty Van Hennekeler has spent four years studying Surra, the disease caused by a parasite that lives in mammalian blood. This parasite, Trypanosoma evansi, causes fever, weakness, and lethargy in its victims and can lead to weight loss, anaemia and even death of infected animals. It is thought this parasite is spread by blood residue remaining on the mouth of the March fly within six hours of feeding from an infected animal. It can also be transmitted by the vampire bat. This parasite is primarily a disease of horses and camels but it can infect a wide range of host animals, causing a wasting disease. The wide host range makes control of this parasite difficult, and there is no vaccination against Surra.

"Surra is not in Australia at the moment but it is of high quarantine risk and a major threat to our biosecurity socially, economically and environmentally," said Van Hennekeler.

The major concern associated with the potential appearance of Surra in Australia is that not only will industries that are dependent upon domestic animals suffer but it would have a significant impact on Australia's native wildlife.

"It appears that marsupials, like wallabies and kangaroos, are severely affected by this disease and suffer a high mortality rate," Van Hennekeler said.

Surra occurs in North Africa, the Middle East, Asia, South America and -- importantly for Australia -- it has recently been discovered in northern Indonesia, East Timor and the Philippines. As a result, officials are concerned that this parasite could possibly reach Australia.

"If it gets to Papua New Guinea, it is conceivable to think that an infected dog or deer could swim between the islands of the Torres Strait and reach the northern tip of Australia," she noted.

Most of Van Hennekeler's study involves monitoring those species of flies in the genus, Tabanus, because they are most likely to be transmitters of Trypanosoma evansi. In collaboration with a team from Murdoch University, she monitors these flies at 11 separate sites along the Cape York Peninsula and also in Townsville because this area poses the highest risk area for potential incursion of the parasite. After nearly two years of work, Van Hennekeler has found 38 Tabanus species at Cape York and eight in Townsville. The three main species she has collected in Townsville were Tabanus townsvilli, Tabanus pallipennis and Pseudotabanus silvester. One of her aims is to establish the flies' seasonal dynamics during the wet seasons.

"I found that the flies were abundant at Lockhart River, the high rainfall making it a really good environment for breeding," she said.

She compared different trapping methods and discovered that the flies were most attracted to carbon dioxide and octenol.

"It makes sense that the flies were attracted to these two," she observed. "CO2 is a by-product of respiration and octenol is basically essence of cow breath. Putting them both together had an even better effect."

Van Hennekeler is now developing a risk model for Trypanosoma evansi that will predict when and where the risk of incursion is the highest so officials can better focus their surveillance efforts.

"The next step is to produce a Geographical Information System (GIS) map combining all the information we have. That is the really exciting bit because in theory someone should be able to look at the map and easily identify where the highest risk if incursion is."

Source:

Genetic Achaeology (quotes).